1. Field of the Invention
The present invention relates to a device for trapping hydrocarbon from an internal combustion engine fuel system and more specifically, to trapping hydrocarbons which would normally be released from an internal combustion engine intake system when the engine is not operating.
2. Disclosure Information
As automotive tailpipe emission controls have become increasingly more stringent, the emission of hydrocarbons from non-tailpipe or non-fuel tank sources has increasingly come under regulation. For example, California Air Resources Board (CARB) regulations applicable to future models specify that automotive vehicles may emit no more that about 0.35 grams of hydrocarbon per day in terms of evaporative emissions. Of this total, fuel-base hydrocarbon may comprise only 0.054 gm. per day. Because the engine's fuel charging system has the job of combining fuel and air, the fuel charging system provides a source from which fuel can escape from the vehicle through the air intake system when the engine is not operating, or in another words, when the engine is shut down. Thus, any hydrocarbons emitted by the fuel injectors, intake manifold walls, cylinders, or positive crankcase ventilation system may leave the engine and enter the ambient through the air induction or air intake system. Thus, emission levels is high as 0.366 gm per day have been recorded from an engine air intake system alone. A fugitive hydrocarbon treatment module according to present invention provides an apparatus and method for significantly reducing fuel hydrocarbon emissions from sources within the engine.
The present module uses zeolite, which comprises crystalline silicon-aluminum oxide structures capable of forming a weak chemical bond with hydrocarbon molecules of the type typically found in motor gasolines and other engine-borne sources. Although zeolite has a lower overall adsorption capacity than some activated carbon materials, zeolite can produce a much stronger interaction with hydrocarbon molecules, which results in a greater efficiency for the zeolite to trap and prevent hydrocarbon from flowing out of an adsorber. Additionally, the zeolite provides advantages upon purging, whereby the zeolite material releases the trapped hydrocarbons in a much more controlled manner than would activated carbon materials. As a result, efficient operation of the engine is not compromised during purging of the trap.
Although U.S. Pat. No. 3,838,673 discloses the use of zeolite to trap vapor, it is noted that the system of the '673 patent will not prevent the emission of vapor emanating from the induction system apart from the carburetor. Similarly, U.S. Pat. No. 5,207,734 also uses zeolite to trap hydrocarbon vapor from the fuel tank and from the engine when the engine is operating, but cannot prevent the emission of hydrocarbon from the internal regions of the engine when the engine is not in operation.
A system and module according to the present invention solves the problems associated with the prior art by providing complete trapping of hydrocarbons when the engine is off, combined with excellent airflow capability and regeneration of the hydrocarbon adsorber during operation of the engine.